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Low Glycemic Index vs. High Fiber Diet: Which is Better for Diabetics?
There's been a lot of talk about low-glycemic-index diets being better for helping diabetics control their blood sugars, but the studies that have been done tend to be small and of short duration. Back in 2008 researchers in Canada decided to improve on past studies by designing a larger, more long term study to compare the effects of a low glycemic index diet with a high cereal fiber diet (JAMA 2008; 300(23):2742-2753).

When the Glycemic Index Doesn't Measure Up
The Glycemic Index is of interest to those seeking to help prevent or treat diabetes because it measures the effect that a specific food has on a person's blood sugar after the person eats it. Unfortunately, the results of studies assessing the link between GI and diabetes risk have been mixed.

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Glycemic Index and Type 2 Diabetes: The Jury's Still Out

Contrary to popular belief, all carbohydrates are not equal when it comes
to how much a food elevates a person's blood sugars. The Glycemic Index
(GI) was created in an effort to rank foods on the effect they have on
an individual's blood sugar levels after they eat that food. The Index
basically measures the difference in response between the food in question
and a reference food - usually a specific glucose solution or a single
slice of white bread. The measure of Glycemic Load (GL) takes into account
the amount of the carbohydrate consumed as well as the food's GI.

Naturally the Glycemic Index has been of great interest to those pursuing
research in diabetes prevention and treatment, but the results of these
studies have been mixed. Some studies show a relationship between diabetes
risk and GI or GL (or both), while others do not. The lack of fully understood
science hasn't stopped the development of commercial diets based on the
Glycemic Index, which include the South Beach diet and Nutrisystem Nourish.

A study published in the British Journal of Nutrition (2011;105(8):1258-1264)
takes another look at dietary GI and GL and the risk of type 2 diabetes.
The researchers made use of information gathered in a 12-year cancer prevention
study in Finland, which included over 25,000 male smokers between the ages
of 50 and 69 years of age. At the start of the study the participants completed
a demographic questionnaire and their height and weight were measured.
They also responded to a detailed diet history questionnaire asking how
often and how much they ate of 276 foods over the previous year.

Using those questionnaires, the researchers were able to calculate each
participant's nutrient intakes as well as GI and GL. They also calculated
the intake of carbohydrates as a percentage of their overall caloric intake
and then that percentage was broken out for low-, medium- and high-GI foods.
The researchers grouped the men into five levels of increasing dietary
GI and five levels of increasing dietary GL.

At the end of the study the researchers compared the diets of those 1098
men who had developed type 2 diabetes with the diets of those who
did not. Interestingly, when the researchers adjusted for age and
intervention group, high GI and GL corresponded with lower risk of
type 2 diabetes. However, when they also adjusted for other variables,
that relationship disappeared. Because they had calculated the percentages
of caloric intake for low-, medium- and high-GI carbohydrates, they
were able to analyze what difference substituting medium-GI carbohydrates
for high-GI carbohydrates might make - which showed a reduction in
risk of type 2 diabetes. On the other hand, substituting low-GI carbohydrates
for high-GI carbohydrates made no difference, while substituting
low-GI carbohydrates for medium-GI carbohydrates actually increased
the risk of type 2 diabetes.

What this means for you

The authors of this study note that this study, showing no relationship,
is in line with other studies that include only men, while other studies
including only women have shown some association between GI, GL and diabetes.
One theory they put forward to explain this difference is that women may
tend to eat more low-GI foods that would have other properties that help
to reduce their risk of diabetes. In any event, it's pretty clear that
the jury is still out on GI, GL and type 2 diabetes risk. Which is not
to say that these measures can not be helpful - only that more studies
need to be done.